So a spa should have a Hartford Loop. The air side of that loop goes to your air inlet. The jet bodies should have the loop plumbed into them along with the water line from the pump pad. When you run water through the jet nozzles, they are designed to pull air in via a venturi effect. The air inlet you will hear a 'glug glug' sound sort of when working. If you put your hand over the air inlet, there should be a suction.
The nozzles should have a sealing surface so the air is pulled in without interference from the water.
When you take one of the nozzles out, take a picture of it and post it.